Sensitive sheet and process for making positives

ABSTRACT

Sheet material having an upper heat-developable layer sensitive to visible light and a lower heat-developable layer sensitive to ultraviolet radiation forms a positive image of an original by a process involving only exposing and heating.

States Patent 1 1 3,607,282

[72] Inventor Edwin A. Grant, Jr. [56] References Cited 2 1 2 Minn- UNITED STATES PATENTS [21] P 5 7 2,725,296 11/1955 Kendall 96/68 [22] F1led Aug.3l, 1966 3,094,417 6/1963 Workman... 96/28 [45] Patented Sept. 21, 1971 [73] Assi nee Minnesota Mining and Manuiacturin 3l434l4 8/1964 Yackel at 96,69 g Company 3 3,392,020 7/l968 Yutzy etal... 96/67 St Paul! Minn 3,409,438 1 1/l968 Lokken 96/95 Primary ExaminerNorman G. Torchin Assistant Examiner-M. F. Kelley [54] SENSITIVE SHEET AND PROCESS FOR MAKING An meyCarpenter, Kinney and Coulter POSIITHVES 7 Claims, 5 Drawing Figs.

52 us. c1 96/69,

96/1 14.1 ABSTRACT: Sheet material having an upper heat-develope- [51 Int. Cl G031: ll/76, ble layer sensitive to visible light and a lower heat-developable G030 1/02 layer sensitive to ultraviolet radiation forms a positive image [50] Field of Search 96/67, 69, of an original by a process involving only exposing and heat- 1l4.l; 117/3638, 36.9; 250/65.l ing.

/6 2 1 f f/lPOJf 70 Z/fiflfi/MQGE SENSITIVE SHEET AND PROCESS FOR MAKING POSITIVES PRODUCT AND PROCESS This invention relates to the recording of light images and in one important aspect makes possible the rapid formation of positive prints by exposure to a light image from a positive original.

The practice of photography ordinarily involves recording a light image from a positive original on a sensitized plate or film as a negative latent image, developing and fixing the visible negative image, exposing a further sensitized sheet through the negative transparency to form a positive latent image, and then developing and fixing the positive print. Two separate wet development steps are required.

A more recent modification of the photographic process for obtaining a positive print from a positive original involves wet development of the latent image obtained from the initial exposure, accompanied by diffusion of unexposed silver salts in solution form to a print-forming surface where the transferred silver is deposited as the desired positive image.

The present invention in its preferred form avoids any necessity of wet development by employing an entirely dry process involving only irradiation and gently heating, to produce positive prints of positive originals. As an example, in the copying of office letters; a copy is obtained in the form of black opaque letters on a white or light-colored background, by a process involving merely irradiation and heating, within not more than a few seconds and without requiring use of any solutions or vapors.

The invention provides a multilayer copy-sheet composite and a method of using the same which is best described in connection with the accompanying drawing in which the several figures illustrate in partial cross section the progress of the composite through the simplified copying process.

FIG. ll illustrates the step of exposure to a light image. Visible light from any convenient source, indicated by the arrows 10, is directed in a pattern, here illustrated as defined by a stencil or mask 11, onto the outer transparent sensitive layer 12 of a copy-sheet composite 16. The layer 12 is supported on a transparent film 13 which in turn overlies and is coextensive with an inner sensitive layer 14 supported on a base or carrier 15. A negative latent image 18 is produced in the layer 12 at the light-struck areas.

The exposed sheet 16 is next subjected to moderate heating as shown in FIG. 2, for example by passing through a heated chamber or by contact with a heated metal plate or roller, here indicated by the wavy arrows 23, and the latent image is thereby developed to an opaque visible image 19 which is a color reversal image of the mask 11.

The sheet is next exposed to radiation indicated by arrows 20 in FIG. 3 and which is conveniently in the ultraviolet or black light region. The radiation passes through the transparent background areas of the outer layer 12 and the transparent film 13 to reach the inner sensitive layer 14 where it creates a latent image 21.

A second heating step then develops the latent image and produces the opaque image 22 in the layer 14 corresponding to the opaque portions of the mask 11, as shown in FIG. 4. At the same time the previously transparent portions of outer layer 12 are also darkened. The combination 16a of film l3 and its uniformly opacified coating 12a is then stripped or lifted from the surface of the imaged layer 14 on the carrier and which forms the final positive copy 16]) corresponding to the original 11.

If desired, the combination of film 13 and imaged coating 12 as shown in FIG. 3 may be recovered as a negative transparency, by removing the same from the remaining structure prior to the final heat development step. Such a subcombination is useful as a mask for making further positives by contact printing methods, or in the projection of light images, or for other purposes.

The radiation-sensitive and heat-developable coatings may contain a light-stable organic silvezr salt, preferably a watchinsoluble silver soap of a long chain fatty acid such as silver behenate or silver stearate, a mild reducing agent such as hydroquinone or methyl gallate, and a catalytic amount of photolytically reducible silver halide such as silver chloride or silver bromide, the latter being formed in situ from the organic silver salt. The coating may contain a film-forming binder such as polyvinyl butyral or cellulose acetate and may be supported on a thin heat-resistant web of paper or plastic film. The silver halide is conveniently formed by briefly exposing the surface of the organic silver city particles or coating to the vapors of one or more halogen acids, or preferably by coating a halogencontaining liquid solution, for example a solution of ammonium bromide or triphenylmethyl bromide, of known small concentration and in controlled amounts over the surface of a thin coating of the organic silver salt. Photosensitizing dyes may be included for increasing the sensitivity to visible light of various wavelengths or may be omitted where exposure to ultraviolet radiation is contemplated. As an illustrative but nonlimiting example, a heavy smooth paper base is first coated with a mix ture of silver behenate powder and polyvinyl butyral in toluene and methylethyl ketone. The coating is dried, and is covered with a further coating of hydroquinone, calcium bromide, and polyvinyl pyrrolidone in methanol and acetone; and the sheet is again dried, the two coatings together forming the radiation-sensitive layer 14 of FIG. 1. Separately, a trans parent thin Mylar polyester film is similarly coated with a first coating of silver behenate and polyvinyl butyral, and a second coating of hydroquinone, calcium bromide, and polyvinyl pyrrolidone to which is added a small proportion of a sensitizing dye, for example Dynacolor R-8l which is 3-allyl'5-[3- ethyl-( 2-naphthoxazoylidene )-ethylidene l -phenyl-2-thiohydantoin, and which extends the sensitivity of the silver salt coating into the range of visible light. These two coatings together form the layer 12 of FIG. l which is sensitive to visible light.

The coated film is superposed over the coated paper to provide the multilayer copy-sheet composite 16. If desired the film may be removably adhered to the coated paper, for example with an intervening thin layer of transparent pressure-sensitive adhesive, for example as indicated by adhesive layer 13' in FIG. 5. In an alternative structure, sheets of the film and paper are hingedly connected along a common edge; or the two in continuous strip form may be wound up together in rolls or folded into packs or sets, one or both preferably being perforated at page-length intervals for convenient removal. The film 13 may be produced as a strippable coating on the coated paper, using a solution of a suitable film-forming polymer in a volatile liquid vehicle which is inert toward the previous coatings.

Exposure of the dyed outer surface of the composite structure to a 14 followed by heating briefly at -l00 C., causes darkening of the outer layer at light-struck areas. The surface is then flooded with radiation in the near ultraviolet, and the entire pack is gain heated. The surface layer becomes entirely darkened. The coated film is then stripped from the coated paper, and the latter is found to be darkened at areas corresponding to the nonlight struck areas of the outer surface in the initial exposure.

It will be seen from the foregoing description that the outer sheet 16a is transparent to, or at least partially transmissive of, that radiant energy by which the inner sensitive layer 14 is converted to the heat-developable or latent image form. At the same time the outer layer 12 is itself sensitive to the effects of radiant energy which has no effect on, or is not transmitted to, the inner layer 14. The outer layer is also heat-convertible, after exposure, to a modification which no longer permits the passage of radiations to which the inner layer is sensitive.

In a variation of the structure and method hereinbefore described, the two photosensitive coatings 12,14 are applied to opposite surfaces of a thin carrier 13 in the absence of any base sheet 15. Thin paper which is visibly opaque but which is readily transmissive of ultraviolet is a preferred example of a carrier 13 in such construction. The outer coating 12 is first exposed to a light image and the sheet is briefly heated to develop the visible image. The sheet is then exposed to ultraviolet light, which is blocked by the developed image but passes through the nonimage areas of the coating 12 and through the carrier 13 to the inner coating 14. Further heating then causes darkening of the thus exposed areas of the inner coating to form a positive image of the original as viewed from the exposed surface of the inner coating. The outer coating may then be removed ifdesired, for example by stripping or by washing, or, where the carrier 13 is visibly opaque, may be allowed to remain in place.

What is claimed is as follows:

. 1. Sheet material adapted for making a positive copy of an original and including an inner layer sensitive to ultraviolet radiation and developable by heating and an outer layer at least partially transmissive of ultraviolet, sensitive to visible light, and developable by heating; each said layer comprising a light-stable water-insoluble organic silver salt, a mild reducing agent, and a catalytically small amount of photolytically reducible silver halide; and said outer layer further including a light-sensitizing dye.

2. Sheet material of claim 1 wherein said inner and outer layers are disposed at opposite surfaces of an intervening thin web which is transmissive of ultraviolet.

3. Sheet material of claim 2 wherein said inner layer is supported on a supporting base. i

4. Sheet material of claim 3 wherein said intervening web is removably adhered to said inner layer.

5. Sheet material of claim 2 wherein said intervening web is visibly opaque.

6. Method of recording a positive image of an original comprising exposing to a visible light image from said original a sheet material as defined in claim 1 to form in said outer layer a latent negative image, heating to develop said latent negative image to a visible image, reexposing to ultraviolet radiation to form in said inner layer a latent positive image, and heating to develop said latent positive image to a visible image.

7. The method of claim 6 including the step of removing the outer layer.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,60Y,282 Dated September 21, 197

Inventor(s) Edwin A. Grant Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 12, after "silver delete "city" and inst-rt --salt-- Column 2, line 5 5, after "a delete "1 and insert -lig;ht-imagc,

Column 2, line 58 after is delete "gain" and insert -again- Signed and sealed this 18th day of April 1972.

(JJILLAL) Attes t iJDvffd'iD BLT-L3 CHEM, JR. MULLSRT G-OTTSCl'iALIL Attoating Officer Commissioner of Patents ORM F'O-1050 (10-59) USCOMM-DC BOB'IB-PBQ v us GOVERNMENT PRINTDNG orrlcs; In! 0-385-334 

2. Sheet material of claim 1 wherein said inner and outer layers are disposed at opposite surfaces of an intervening thin web which is transmissive of ultraviolet.
 3. Sheet material of claim 2 wherein said inner layer is supported on a supporting base.
 4. Sheet material of claim 3 wherein said intervening web is removably adhered to said inner layer.
 5. Sheet material of claim 2 wherein said intervening web is visibly opaque.
 6. Method of recording a positive image of an original comprising exposing to a visible light image from said original a sheet material as defined in claim 1 to form in said outer layer a latent negative image, heating to develop said latent negative image to a visible image, reexposing to ultraviolet radiation to form in said inner layer a latent positive image, and heating to develop said latent positive image to a visible image.
 7. The method of claim 6 including the step of removing the outer layer. 